Peristaltic pump for imaging apparatus

ABSTRACT

A pump for pumping fluid using peristaltic compression. The pump includes a rotor and a roller. The rotor includes a first cam that extends along a circumferential direction relative to the rotor. The first cam has first and second dwells. The roller is movable relative to the rotor between the first dwell and the second dwell of the first cam as the rotor rotates in a first direction and a second direction. The rotor includes a second cam extending radially from its shaft for engaging the roller. Contact between the second cam and the roller increases frictional resistance between the rotor and the roller as the roller translates between the first and second dwells of the first cam such that the roller transitions between the first and second dwells without slipping.

FIELD OF THE INVENTION

The present invention relates to micro-fluid applications, such as inkjet printing. More particularly, it relates to peristaltic pumps used in inkjet printers.

BACKGROUND

The art of printing images with micro-fluid technology is relatively well known. One common type of inkjet printer uses a replaceable print cartridge having a printhead and a supply of ink contained within the cartridge to record text and images on a print media. The printhead typically moves on a printhead carrier relative to a media path and a control system activates the printhead to selectively eject ink droplets onto the print media in a pattern of pixels corresponding to images being printed. When the supply of ink contained within the print cartridge is depleted, the print cartridge is disposed and a new print cartridge is installed in the printhead carrier.

Another type of inkjet printer utilizes an off-carrier ink supply system where ink is supplied from a remote ink source typically housed in an off-carrier ink supply tank not mounted on the printhead carrier. Ink is delivered to the printhead by continuous or intermittent siphoning or pumping of ink from the ink supply tank through a flexible supply conduit or tube.

In the off-carrier ink supply system, nozzle prime functions are required in order for the printhead to operate properly. Peristaltic pumps are typically used in maintenance stations that require a vacuum to facilitate nozzle prime functions. In some designs, a section of the tube is fitted inside a circular pump casing and a cam surface is used to engage or disengage a pump roller from the tube by rotational motion of a rotor. In particular, the roller moves between two positions, a vent position and a pump position defined by two ends of the cam surface, depending on the direction of rotation of the rotor. In the pump position, the roller is positioned at a distance from the center of the rotor sufficient enough for it to engage and compress the tube. As the rotor turns, the part of the tube under compression occludes thus forcing fluid to flow through the tube. When the rotor turns in the opposite direction, the roller moves towards the other end of the cam surface and is brought closer to the center of the rotor such that it can no longer compress the tube. This is done to either vent the pump and/or to unocclude the tube for increased pump tube life.

For motor efficiency and better acoustics, it is better to have rollers with low rolling resistance. However, this also provides small frictional force between the cam and roller when the roller transitions between the two positions. Consequently, the roller becomes liable to slip along the cam surface which may result to the roller not easily transitioning up the cam and fully occluding the tube.

Accordingly, a need exists in the art to increase the frictional force imparted to the roller as it transitions between the vent and pump positions while maintaining low friction at the vent and pump positions. Additional benefits and alternatives are also sought when devising solutions.

SUMMARY

The above-mentioned and other problems become solved with pumps having features that increase frictional resistance between rotors and rollers as rollers transition between functional positions on rotors.

In a representative embodiment, the pump includes a body having an inner surface defining a hollow portion, a tubing arranged to extend along the inner surface, a rotor, and a roller. The rotor includes a first cam that extends along a circumferential direction relative to the rotor. The first cam has a first dwell and a second dwell. The roller is movable relative to the rotor between the first dwell and the second dwell of the first cam as the rotor rotates in a first direction and a second direction, respectively. The roller is operative to allow the tubing to be vented when positioned in the first dwell of the first cam in which the roller member unoccludes the tubing as the rotor is rotated in the first direction. On the other hand, the roller is operative to compel fluid to flow through the tubing when positioned in the second dwell of the first cam in which the roller occludes the tubing against the inner surface as the rotor is rotated in the second direction.

In one example embodiment, the rotor includes at least one second cam extending radially from its shaft for engaging the roller member. Contact between the at least one second cam and the roller member increases frictional resistance between the rotor and the roller as the roller translates between the first and second dwells of the first cam such that roller transitions between the first and second dwells without slipping. When positioned at the first and second dwells of the first cam, the roller frees itself from any contact with the at least one second cam to maintain low friction.

In another example embodiment, an annular ring is disposed at an end of the roller. A third cam is disposed at a longitudinal end of the shaft and extends along a circumferential direction relative to the rotor and adjacent the end of the roller. The annular ring engages the second cam so as to increase frictional resistance as the roller translates between the first and second dwells of the first cam.

In an alternative embodiment, a gear is attached to an end of the roller. A gear section is disposed at a longitudinal end of the shaft and extends along a circumferential direction relative to the rotor and adjacent the end of the roller.

The gear of the roller meshes with the gear section as the roller translates between the first and second dwells of the first cam such that the roller translates between the first and second dwells of the first cam without slipping.

Both annular ring and gear are free from contact with the third cam and gear section, respectively, when the roller is positioned in the first and second dwells of the first cam. As such, frictional resistance is increased as the roller moves between the first and second dwells while low friction is maintained at the first and second dwells.

These and other embodiments are set forth in the description below. Their advantages and features will become readily apparent to skilled artisans. The claims set forth particular limitations.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings incorporated in and forming a part of the specification, illustrate several aspects of the present invention, and together with the description serve to explain the principles of the invention. In the drawings:

FIG. 1 is a diagrammatic view in accordance with the present invention showing a printhead carrier system;

FIG. 2 is a schematic view of an off-carrier ink supply system;

FIG. 3 is a cross-sectional view of a peristaltic pump used in the off-carrier ink supply system of FIG. 2.

FIG. 4 is a perspective view of the peristaltic pump in FIG. 3;

FIG. 5 is an exploded view of a rotor member and a roller member of the peristaltic pump shown in FIG. 4;

FIGS. 6A-6C are side views and cross-sectional views showing the roller member at different positions relative to the rotor member in FIG. 3;

FIG. 7 is a perspective view illustrating a rotor member according to another embodiment; and

FIG. 8 is a perspective view illustrating a rotor member according to another example embodiment.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

In the following detailed description, reference is made to the accompanying drawings where like numerals represent like details. The embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. It is to be understood that other embodiments may be utilized and that process, electrical, and mechanical changes, etc., may be made without departing from the scope of the invention. The following detailed description, therefore, is not to be taken in a limiting sense and the scope of the invention is defined only by the appended claims and their equivalents. In accordance with embodiments of the invention, pumps using peristaltic compression include features that increase frictional resistance between a roller and a rotor as the roller transitions between functional positions on the rotor to overcome slipping problems associated with the roller.

With reference to FIG. 1, a printhead carrier system 10 for use in an imaging device includes a carrier 15 mounting one or more disposable or (semi) permanent printheads 20. Carrier 15 is arranged to be driven by a motor 25 along a shaft 30 that defines a bi-directional scanning path 33. At a directive of a controller 35, motor 25 moves the carrier 15 in a controlled manner along bidirectional scanning path 33 and across a sheet of print media 35 during a printing operation.

In FIG. 2, an off-carrier ink supply system 50 is utilized to continuously supply printhead 20 with ink. Constant fluid communication between a remote ink supply tank 55 and printhead 20 is maintained by way of an ink supply line 60. Ink is delivered to printhead 20 by continuous siphoning of ink from remote ink supply tank 55 through ink supply line 60. Subsequently, in the event of ink exhaustion or depletion, ink supply in the off-carrier ink supply system 50 may be renewed by replacing ink supply tank 55 or refilling same with ink.

In order to conduct printhead servicing or maintenance operations, controller 35 controls the movement of carrier 15 to position printhead 20 in relation to a maintenance station 65. Maintenance station 65 defines a maintenance area provided for performing printhead maintenance or servicing operations on nozzles of printhead 20. Such operations may include, for example, spit maintenance operations, wiping operations, and capping operations. Other services, such as priming and suction, may also be performed by the inclusion of vacuum devices such as vacuum pumps.

When printhead priming is required, printhead 20 is positioned by carrier 15 over maintenance station 65 and in sealing engagement with a printhead cap 70. Cap 70 is fluidly connected to a vacuum canister 75 via a conduit 80. A first pinch valve 85 is disposed at an intermediate portion of conduit 80 for controlling the flow of fluid through conduit 80 between printhead cap 70 and vacuum canister 75. Printhead 20 is also fluidly connected to vacuum canister 75 via an air vent tube 90 which is coupled to a second pinch valve 95 used to control the flow of fluid through air vent tube 90. A fluid tubing 100, typically a flexible conduit or tube, fluidly connects vacuum canister 75 to a waste ink container 105. Fluid tubing 100 has an intermediate section 100A (FIG. 3) engaged within a peristaltic pump 110. Fluid flowing through fluid tubing 100 enters pump 110 at an upstream opening 205 and leaves pump 110 at a downstream opening 210. Pump 110 is used to draw fluid, i.e., air and/or ink, from the vacuum canister 75 into the waste ink container 105 upon activation of pump motor 115 by controller 35.

During initial printhead priming, such as when the imaging device is first set up or after replacement of printhead 20, first pinch valve 85 opens conduit 80 while second pinch valve 95 pinches air vent tube 90. When pump 110 is activated, ink is pumped from ink supply tank 55 through ink supply line 60 and into printhead 20. Eventually, ink and/or air bubbles are drawn out of the nozzles of printhead 20 and are directed to vacuum canister 75. The ink and/or air bubbles are then drained to waste ink container 105 by pump 110. Pumping may continue for a predetermined period necessary to fully prime printhead 20.

Even if printhead 20 has already been primed, priming operations may still be required to remove air bubbles which may accumulate after the last priming operation. In subsequent priming operations, first pinch valve 85 is controlled to restrict fluid flow along conduit 80 while second pinch valve 95 is opened. As ink from ink supply line 60 flows into carrier 15 when pump 110 is turned on, air and/or bubbles are directed toward a vacuum chamber (not shown) located above printhead 20 and fluidly connected to air vent tube 90. Thereafter, air is suctioned from the vacuum chamber through air vent tube 90 and directed toward vacuum canister 75 and into the waste ink container 105 by pump 110. Pumping may continue for a predetermined period necessary to remove substantially all air bubbles from the ink supply system and fully prime printhead 20.

During use, pump 110 repetitively compresses and pressurizes intermediate section 100A to compel fluid to flow through fluid tubing 100. The repetitive compression of the intermediate section 100A produces negative pressure in the cap 70 or the vent tube 90 which causes ink and/or air from printhead 20 or the vacuum chamber to be drawn out into conduit 80 or vent tube 90. The ink and/or air flow through conduit 80 or vent tube 90, into vacuum canister 75, and are gradually drained to the waste ink container 105 by pump 110.

In contrast, when priming or suction is not required, pump 110 disengages intermediate section 100A and is switched off. Hence, no ink and/or air are drawn out of printhead 20 or the vacuum chamber. This also prevents deformation of the flow area of intermediate section 100A and extends the life of fluid tubing 100.

The above functionality is achieved by the use of a pump roller that is movable relative to a pump rotor and configured to selectively engage or disengage intermediate section 100A based on its position on the pump rotor. Movement of the pump roller between one position, such as a pressurizing position during use of pump 110, and another position, such as a disengaged position when pump 110 is not in use, is facilitated by rotational motion of the pump rotor and friction forces between the pump roller and the pump rotor. Increased friction forces prevent slipping of the pump roller against the pump rotor which allows successful transitioning of the pump roller between positions.

FIG. 3 shows pump 110 designed to selectively compress intermediate section 100A. A cam 280 supports a roller 230 that is movable along cam 280, as indicated by arrow 107, between a first position P1 and a second position P2. First position P1 represents a “non-pressing” or vent position when pump 110 is not in use. On the other hand, second position P1 represents a “pressing” or pump position when pump 110 is in use during priming or suction operations.

At position P1, roller 230 is positioned at a distance D1 from the center 112 of pump 110. In this position, roller 230 does not reach intermediate section 100A or, alternatively, contacts intermediate section 100A with a pressing force that is insufficient to cause occlusion of fluid tubing 100 against a wall 215. As such, roller 230 operatively allows fluid tubing 100 to be vented while positioned at the vent position P1.

At position P2, roller 230 is positioned at a distance D2, greater than distance D1, from the center 112 and closer to wall 215 compared to when it is in vent position P1. The difference between distances D1 and D2 is attributed to the profile of cam 280 having a center that is offset and not concentric with the center 112 of pump 110. While in this position, roller 230 pinches a portion of intermediate section 100A against wall 215 of pump 110. This creates a pinch 100B and subjects intermediate section 100A to occlusion, in contrast to when roller 230 is at position P1 where intermediate section 100A is open and not pinched.

When cam 280 is rotated about the center 112 of pump 110 in a clockwise direction 117, frictions between roller 230, fluid tubing 100 and cam 280 cause roller 230 to move from position P1 to position P2. As cam 280 is further rotated in the clockwise direction 117, cam 280 forces roller 230 to rotate therewith and compress intermediate section 100A against wall 215 during its rotation to impart motive force to fluid contained within fluid tubing 100.

Rotating cam 280 in a counter-clockwise direction 119, on the other hand, moves roller 230 back to the vent position P1 with the aid of frictions between roller 230, fluid tubing 100, and cam 280. As such, the transitioning of roller 230 between positions P1 and P2 is facilitated by opposite pump rotations as well as frictions between roller 230, cam 280, and intermediate section 100A of fluid tubing 100. However, friction between roller 230 and cam 280 may not be sufficient enough to aid in the transitioning of roller 230 as they are typically made of low friction materials for reasons of increasing pump efficiency. This may present less overall friction to aid in the transitioning and cause slippage between roller 230 and cam 280. As such, additional sources of friction may be needed to facilitate the transitioning in order to prevent or avoid slippage.

In accordance with example embodiments of the present disclosure, peristaltic pump 110 includes features that help overcome slippage between roller 230 and cam 280. With reference to FIGS. 4-5, peristaltic pump 110 has a pump housing or body 200 that houses the intermediate section 100A of fluid tubing 100 within a hollow portion 203 thereof. Pump body 200 includes upstream opening 205 where fluid flowing through fluid tubing 100 enters pump 110, and downstream opening 210 where fluid flowing through fluid tubing 100 exits pump 110. The intermediate section 100A of fluid tubing 100 extends along inner wall or surface 215 of the hollow portion 203 from the upstream opening 205 to the downstream opening 210. Intermediate section 100A forms a loop within pump body 200 and has sections that partially overlap at an area between the upstream opening 205 and downstream opening 210. A rotor member 220 is mounted rotatably relative to pump body 200 and includes a rotor shaft 225 defining a rotational axis 227 of rotor member 220. Roller member 230 is movably mounted relative to the rotor member 220 and is configured to either engage or disengage the intermediate section 100A of fluid tubing 100 upon rotation of rotor member 220, as discussed above.

Rotor member 220 includes circular wheels 240, 245 at opposite longitudinal ends of rotor shaft 225. One of circular wheels 240, 245 is operatively coupled to pump motor 115 for driving pump 110. A pivot frame 250 is disposed between circular wheels 240, 245 and includes an upper frame section 253 and a lower frame section 255 connected to each other by supports 257, 259. The upper and lower frame sections 253, 255 have pivot pins 260 that are inserted into corresponding holes 263 formed on wheels 240, 245 thereby pivotably mounting pivot frame 250 about a pivot axis 247. A rib 265 also extends between circular wheels 240, 245. A spring 270 (FIG. 5) is disposed between rib 265 and support 259 to continuously urge pivot frame 250 to pivot about pivot axis 247 and assist roller member 230 in compressing fluid tubing 100, as will be explained in more detail below.

Upper frame section 253 defines primary cam 280 having a first dwell 283 and a second dwell 285 spaced apart in the circumferential direction of rotor member 220 and eccentric relative to the rotational axis 227 of rotor member 220. In particular, the radial distance of the first dwell 283 from the rotational axis 227 of the rotor member 220 is less than the radial distance of the second dwell 285 from the rotational axis 227, corresponding to distances D1 and D2 in FIG. 3. The differences in radial distances of first dwell 283 and second dwell 285 allows roller member 230 to be positioned at different radial distances from rotational axis 227 thereby allowing roller member 230 to selectively engage intermediate section 100A depending on its relative position on rotor member 220. On the other hand, lower frame section 255 defines a curved guide slot 290 having a profile consistent with that of primary cam 280. During transitioning of roller member 230 between the vent and pump positions, roller member 230 moves along cam 280 and guide slot 290.

Roller member 230 includes a cylindrical body 300 and a roller shaft 305, and is supported by the upper frame section 253 and lower frame section 255 of pivot frame 250. The ends of roller shaft 305 project from both ends of cylindrical body 300. The first end 307 of roller shaft 305 inserts through guide slot 290 while its second end 309 is arranged in the primary cam 280 such that roller member 230 is movable between the first and second dwells 283, 285 of primary cam 280 and first and second ends 293, 295 of guide slot 290. The dwells and ends of primary cam 280 and guide slot 290 define the two operating or functional positions, corresponding to positions P1 and P2 in FIG. 3, where roller member 230 disengages or engages fluid tubing 100. In particular, first dwell 283 and first end 293 define the vent position where cylindrical body 300 of roller member 230 does not occlude fluid tubing 100 due to disengagement with or insufficient pressing force imparted onto intermediate section 100A as shown in FIG. 3. Second dwell 285 and second end 295 define the pump position where cylindrical body 300 occludes fluid tubing 100 due to its radially outer position relative to rotational axis 227 and its pinching engagement with intermediate section 100A as shown in FIG. 3.

Primary cam 280, guide slot 290, and/or roller shaft 305 are made from materials having relatively small coefficient of friction such that frictional resistance at both functional positions is reduced. This advantageously reduces torque or force required to rotate rotor member 220 when actuating pump 110 and improve pump efficiency. Due to the low frictional resistance, however, it may be difficult for roller member 230 to easily transition between the two functional positions, as previously mentioned. For example, the low frictional resistance may cause roller member 230 to slip along the primary cam 280 and/or guide slot 290 and not transition to the other functional position. In other possible cases, rotor member 220 may have to rotate a number of times before causing roller member 230 to properly transition from one functional position to another.

To prevent slipping action, one or more secondary cams 320 are arranged to extend radially from the rotor shaft 225 between the circular wheels 240, 245 to help roller member 230 transition between the two functional positions. In the example shown, two secondary cams 320 are symmetrically arranged relative to the longitudinal center of roller shaft 305 such that friction forces caused by contact between secondary cams 320 and roller member 230 remain substantially balanced about the longitudinal center of roller member 230. Alternatively, one or more than two secondary cams 320 may be disposed along roller shaft 305 and arranged in such a manner that forces are balanced about the longitudinal center of roller member 230. The symmetrical arrangement of the secondary cams 320 eliminates creation of moment about the longitudinal center of roller member 230 which may induce skewing of roller member 230 upon its transition between the functional positions. Thus, roller member 230 may remain substantially parallel relative to the rotational axis 227of the rotor member 220 during its transition. It is understood, however, that the symmetrical arrangement is not a requirement and that having secondary cams that are not evenly positioned about the longitudinal center of roller member 230 is equally practicable.

Secondary cams 320 have surfaces with relatively higher coefficient of friction compared to that of primary cam 280. As such, contact between the secondary cams 320 and cylindrical body 300 during the transition helps increase the frictional resistance between roller member 230 and rotor member 220, thereby allowing roller member 230 to easily transition between the functional positions without slipping.

The profile of the secondary cams 320 is shaped in such a manner that it is contacted by the cylindrical body 300 only during the transition of the roller member 230 between the vent and pump positions, as shown in FIG. 6B. At times where roller member 230 is positioned in one of the vent and pump positions, i.e., when roller shaft 305 is positioned in the first dwell 283 or second dwell 285 of primary cam 280, respectively, secondary cams 320 are free from any contact with the cylindrical body 300, as shown in FIGS. 6A and 6C. In this way, frictional resistance at the functional positions is kept considerably low since the only existing frictional force that rotor member 220 imparts on roller 230 is the relatively low friction between roller shaft 305 and cam 280.

The operation of peristaltic pump 110 will now be described. FIG. 6A shows roller member 230 initially in the vent position. When pump motor 115 is activated and rotor member 220 rotates in the clockwise direction illustrated by arrow 117, friction between cylindrical body 300 and fluid tubing 100 causes roller member 230 to roll up to the secondary cams 320, as shown in FIG. 5B. As rotor member 220 further rotates in the same direction, increased frictional resistance due to contact between the cylindrical body 300 and secondary cams 320 causes roller member 230 to further translate towards the pump position without much difficulty while gradually pressing and squeezing the intermediate section 100A of fluid tubing 100. Eventually, roller member 230 reaches the pump position, as shown in FIG. 5C. Rotating rotor member 220 in the clockwise direction 117 while roller member 230 is in the pump position causes peristaltic compression of intermediate section 100A thereby compelling movement of fluid within fluid tubing 100. Spring 270 provides a spring force that continuously urges pivot frame 280 to pivot about pivot axis 263 toward direction 117 so as to ensure that roller member 230 sufficiently compresses and fully occludes intermediate section 100A. Fluid is thus compelled to flow through fluid tubing 100, drawing ink and/or air in and out of printhead 20, directing the ink and/or air to vacuum canister 75, and into waste ink container 105.

When pump motor 115 is activated to rotate rotor member 220 in the counter-clockwise direction opposite the direction illustrated by arrow 117, friction between cylindrical body 300 and fluid tubing 100 causes roller member 230 to roll up to the secondary cams 320 from the pump position shown in FIG. 5C. As rotor member 220 further rotates in the counter-clockwise direction, increased frictional resistance due to contact between the cylindrical body 300 and secondary cams 320 causes roller member 230 to further translate towards the vent position without much difficulty while gradually releasing intermediate section 100A of fluid tubing 100 from occlusion. Eventually, roller member 230 positions itself back in the vent position, as shown in FIG. 5A.

Additionally, frictional resistance to aid in the transitioning of the roller member 230 may further be increased by implementing a tertiary cam 400 on the lower frame section 255 adjacent guide slot 290, as shown in FIG. 7. An annular ring member 405, such as an O-ring, is disposed at the first end 307 of roller shaft 305. Similar to the secondary cams 320, tertiary cam 400 functions to increase frictional resistance between roller member 230 and rotor member 220 as roller member 230 transitions between the vent and pump positions. Tertiary cam 400 extends along the circumferential direction of rotor member 220 and is shaped in such a manner that it is free from any contact with the annular ring member 405 when roller shaft 305 is positioned in the first dwell 283 and second dwell 285 of primary cam 280. Annular ring member 405 only contacts tertiary cam 400 during transition so that friction is increased only during transition while low friction is maintained in the operating or functional positions of roller member 230.

In FIG. 6, an alternative embodiment provides a gear 505 attached to the first end 307 of roller shaft 305 instead of annular ring member 405. Accordingly, tertiary cam 400 is replaced with a gear section 500 that meshes with the gear 505 of roller member 230 as roller member 230 transitions between the vent and pump positions. Like the tertiary cam 400, gear section 500 extends along the circumferential direction of rotor member 220 and is shaped in such a manner that its teeth are free from any contact with the teeth of gear 505 when roller shaft 305 is positioned in the first dwell 283 and second dwell 285 of primary cam 280. As such, low friction is maintained in the vent and pump positions of roller member 230 while slippage is prevented during the transitioning of the roller.

With the above features, frictional resistance is increased as the roller member 230 moves from one functional position to another. Secondary cams 320, tertiary cam 400, or gear section 500 only contact with roller member 230 or parts thereof as roller member 230 moves between the vent and pump positions such that low friction is maintained in the vent and pump positions. It is understood that the different embodiments may be implemented individually or in various combinations as would occur to those skilled in the art, and that combinations thereof results to more increased frictional resistance to aid in the transitioning of roller member 230 between the vent and pump positions.

The foregoing illustrates various aspects of the invention. It is not intended to be exhaustive. Rather, it is chosen to provide the best illustration of the principles of the invention and its practical application to enable one of ordinary skill in the art to utilize the invention, including its various modifications that naturally follow. All modifications and variations are contemplated within the scope of the invention as determined by the appended claims. Relatively apparent modifications include combining one or more features of various embodiments with features of other embodiments. 

1. A pump for pumping fluid using peristaltic compression, comprising: a body including an inner surface defining a hollow portion; a tubing arranged to extend along the inner surface; a rotor including a shaft defining a rotational axis thereof, and a first cam extending along a circumferential direction relative to the rotor, the first cam having a first dwell and a second dwell; and a roller movable relative to the rotor between the first dwell and the second dwell of the first cam as the rotor rotates about the rotational axis in a first direction and a second direction, the roller operative to allow the tubing to be vented when positioned in the first dwell of the first cam in which the roller unoccludes the tubing as the rotor is rotated in the first direction and to compel fluid to flow through the tubing when positioned in the second dwell of the first cam in which the roller occludes the tubing against the inner surface as the rotor is rotated in the second direction, wherein the rotor includes at least one second cam extending radially from the shaft for engaging the roller so as to increase frictional resistance between the rotor and the roller as the roller translates between the first and second dwells of the first cam.
 2. The pump of claim 1, wherein the roller is free from any contact with the at least one second cam when positioned in the first and second dwells of the first cam.
 3. The pump of claim 1, wherein a first frictional force between the roller and the at least one second cam is greater than a second frictional force between the roller and the first cam.
 4. The pump of claim 1, further comprising an annular ring disposed at an end of the roller, the rotor further including a third cam extending along a circumferential direction relative to the rotor and adjacent the end of the roller such that the annular ring engages the third cam so as to increase frictional resistance between the rotor and the roller as the roller translates between the first and second dwells of the cam.
 5. The pump of claim 4, wherein the annular ring is free from any contact with the third cam when the roller is positioned in the first and second dwells of the first cam.
 6. The pump of claim 4, wherein a first frictional force between the annular ring and the third cam is greater than a second frictional force between the roller and the first cam.
 7. The pump of claim 4, wherein the annular ring includes an o-ring.
 8. The pump of claim 1, further comprising a gear attached to an end of the roller, the rotor further including a gear section extending along a circumferential direction relative to the rotor and adjacent the end of the roller such that the gear of the roller meshes with the gear section as the roller translates between the first and second dwells of the first cam.
 9. The pump of claim 8, wherein the gear of the roller is free from any contact with the gear section when the roller is positioned in the first and second dwells of the first cam.
 10. A peristaltic pump, comprising: a housing having an inner wall; a tubing arranged to extend along the inner wall; a rotor rotatably mounted in the housing and including a shaft defining a rotational axis of the rotor; a first cam disposed at a first longitudinal end of the shaft and extending along a circumferential direction relative to the rotor, the first cam having a first dwell and a second dwell that are eccentric relative to the rotational axis of the rotor; a roller movable relative to the rotor between the first dwell and the second dwell of the first cam as the rotor rotates in a first direction and a second direction, the roller operative to allow the tubing to be vented when in the first dwell of the first cam in which the roller unoccludes the tubing as the rotor is rotated in the first direction and to compel fluid to flow through the tubing when in the second dwell of the first cam in which the roller occludes the tubing against the inner wall as the rotor is rotated in the second direction; an annular ring disposed at an end of the roller; and a second cam disposed at a second longitudinal end of the shaft and extending along a circumferential direction relative to the rotor and adjacent the end of the roller such that the annular ring engages the second cam so as to increase frictional resistance as the roller translates between the first and second dwells of the first cam.
 11. The peristaltic pump of claim 10, wherein the annular ring is free from any contact with the second cam when the roller is positioned in the first and second dwells of the first cam.
 12. The peristaltic pump of claim 10, wherein a first frictional force between the annular ring and the second cam is greater than a second frictional force between the roller and the first cam.
 13. The peristaltic pump of claim 10, wherein the annular ring includes an o-ring.
 14. The peristaltic pump of claim 10, wherein the rotor further includes at least one third cam extending radially from the shaft for engaging a central portion of the roller so as to substantially increase frictional resistance between the rotor and the roller as the roller translates between the first and second dwells of the first cam.
 15. The peristaltic pump of claim 14, wherein the at least one third cam causes the roller to remain substantially parallel relative to the rotational axis of the rotor when the roller transitions between the first and second dwells of the first cam.
 16. The peristaltic pump of claim 14, wherein the roller is free from any contact with the at least one third cam when positioned in the first and second dwells of the first cam.
 17. A peristaltic pump, comprising: a housing having an inner wall; a tubing arranged to extend along the inner wall; a rotor rotatably mounted in the housing and including a shaft defining a rotational axis thereof; a first cam disposed at a first longitudinal end of the shaft and extending along a circumferential direction relative to the rotor, the first cam having a first dwell and a second dwell that are eccentric relative to the rotational axis of the rotor; a roller movable relative to the rotor between the first dwell and the second dwell of the first cam as the rotor rotates in a first direction and a second direction, the roller operative to allow the tubing to be vented when positioned in the first dwell of the first cam in which the roller unoccludes the tubing as the rotor is rotated in the first direction and to compel fluid to flow through the tubing when positioned in the second dwell of the first cam in which the roller occludes the tubing against the inner wall as the rotor is rotated in the second direction; a gear attached to an end of the roller; and a gear section disposed at a second longitudinal end of the shaft and extending along a circumferential direction relative to the rotor and adjacent the end of the roller such that the gear of the roller meshes with the gear section as the roller translates between the first and second dwells of the first cam.
 18. The peristaltic pump of claim 17, wherein the gear of the roller is free from any contact with the gear section when the roller is positioned in the first and second dwells of the first cam.
 19. The peristaltic pump of claim 17, further comprising at least one second cam extending radially from the shaft for engaging a central portion of the roller so as to substantially increase frictional resistance between the rotor and the roller as the roller translates between the first and second dwells of the first cam.
 20. The peristaltic pump of claim 19, wherein the roller is free from any contact with the at least one second cam when positioned in the first and second dwells of the first cam.
 21. A peristaltic pump, comprising: a body including an inner surface defining a hollow portion; a tubing arranged to extend along the inner surface; a rotor including a shaft and a first cam at a longitudinal end of the shaft extending along a circumferential direction relative to the rotor, the rotor being rotatable within the hollow portion about a rotational axis defined by the shaft and the first cam having a first dwell and a second dwell; and a roller movable relative to the rotor between the first dwell and the second dwell of the first cam as the rotor rotates in a first direction and a second direction, respectively, the roller operative to allow the tubing to be vented when positioned in the first dwell of the first cam in which the roller unoccludes the tubing as the rotor is rotated in the first direction, and to compel fluid to flow through the tubing when positioned in the second dwell of the first cam in which the roller occludes the tubing against the inner surface as the rotor is rotated in the second direction; wherein the rotor includes at least one second cam extending radially from the shaft for engaging a central portion of the roller so as to increase frictional resistance between the rotor and the roller as the roller translates between the first and second dwells of the first cam. 